Provides some further examples on using environment variables. (#1)

Author: robinbryce

env-var-templating/README.md

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+# Environment Variables
+
+Supplimental, examples of setting, overriding and constructing environment
+variables. There is nothing special about showenv.sh, it is simply a place
+holder for an external program. echo would do just as well
+

env-var-templating/Taskfile.yml

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+# CGO environment variables are used as a motivating example.
+
+flexible:
+  # A task intended to be extended or called by others. Note the use of yaml
+  # anchors "&flexible_env"
+  cmds:
+    - ./showenv.sh
+  env: &flexible_env
+    # OTHERPATH defaults to the emptystring in Taskvars.yml, and can be set
+    # on the command line: OTHERPATH=other/path/ task flexible
+    # Or in any task calling or extending this one
+    CGO_LDFLAGS: "-L{{.OTHERPATH}}some/path/lib {{- range $_, $libname := .LIBNAMES | splitLines}}{{if $libname}} -l{{$libname}}{{end}}{{end}}"
+  vars:
+    LIBNAMES: |
+      aaa
+      bbb
+      ccc
+
+calling:
+  cmds:
+    - task: flexible
+      vars:
+        LIBNAMES: |
+          xxx
+          yyy
+
+extending:
+  cmds:
+    - ./showenv.sh
+  env:
+    <<: *flexible_env
+    CGO_ANOTHER_VAR: "extending env key, this is a shallow merge"
+  vars:
+    # These variables override any pulled in from flexible_env
+    LIBNAMES: |
+      ddd
+      eee
+
+
+envproperty:
+  cmds:
+    - ./showenv.sh
+  env:
+    CGO_LDFLAGS: "-L/some/path -laaa -lbbb -lccc"
+
+possible:
+  # Notice the quotes guarding the variable references on the second line of
+  # the cmds.
+  cmds:
+    - |
+      CGO_LDFLAGS="-L/some/path -laaa -lbbb -lccc"
+      CGO_LDFLAGS="$CGO_LDFLAGS" ./showenv.sh "$CGO_LDFLAGS"
+
+wrong:
+  # In this instance the quotes are missing, the output will be:
+  #
+  # CGO_LDFLAGS=-L/some/path-laaa-lbbb-lccc
+  # $@=-L/some/path-laaa-lbbb-lccc
+  cmds:
+    - |
+      CGO_LDFLAGS="-L/some/path -laaa -lbbb -lccc"
+      CGO_LDFLAGS=$CGO_LDFLAGS ./showenv.sh $CGO_LDFLAGS

env-var-templating/Taskvars.yml

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+OTHERPATH: ""

env-var-templating/showenv.sh

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+#!/bin/bash
+env | grep CGO_
+echo "\$@=$@"